The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: andy on 02.10. 2012 19:30

Title: sprockets
Post by: andy on 02.10. 2012 19:30

what teeth sprockets are people useing?????? to make the argument/discusion more intresting its bloody hilly where i live and ill be 2up most of the time....yes the wife likes been on the back of bikes   *whistle* *whistle* *whistle*

Title: Re: sprockets
Post by: chaterlea25 on 02.10. 2012 20:38

Hi Andy,
Sprocket sizes are dependant on a fair few factors??
There have been some previous discussions on this in older posts
Anyway,
What bike are you talking about?
What state of tune is the engine in?
What weight are rider and passenger?
What size rear tyre is fitted?

John O R

Title: Re: sprockets
Post by: andy on 03.10. 2012 09:27

engine is a A10 in good to excellent order and sound combined weight about 30stone standed tyre...cheers

Title: Re: sprockets
Post by: chaterlea25 on 03.10. 2012 11:50

Hi Andy,
Assuming a late A10 with standard  19 and 42t gbox and rear sprockets
You could probably run with a 22t engine sprocket easily,
I find anything less produces a very buzzy engine
I fitted a 23t to a friends standard A10 recently and it has a 110 x 19 roadrider rear tyre
He is very happy with the gearing for one up use,
The southwest of Ireland is All hills  *smile*
I recently fitted a 24t to my SR and it fly's on it, this engine is to RGS spec though + high flow valves etc
It will still be accelerating hard when I get near the top of a local hill which has a long hard incline  *eek*
It needs more use of the gearbox two up on the back road hills than before though
HTH
John O R

Title: Re: sprockets
Post by: andy on 03.10. 2012 13:37

thats really usefull cheers very much. wink2

Title: Re: sprockets
Post by: JulianM on 03.10. 2012 15:00

I have a 21T on my Scrambler  BUT a 60 on the rear  *smile* *smile*

Should accelerate well  ;)

Julian

Title: Re: sprockets
Post by: Butch (cb) on 04.10. 2012 13:21

Is the ratio on the primary drive always the same then or should that be factored in?

Title: Re: sprockets
Post by: chaterlea25 on 04.10. 2012 17:53

Hi cyclobutch,
If you read my post agian you will see I was on about changing the engine sprocket (the one on the craankshaft)
Its a lot easier to change the crank sprocket so this changes the primary ratio.
The "normal" sprockets on the gearbox and rear wheel on a late A10 are 19 and 42
this gives a ratio of 2.211:1
primary ratio of for example 22t o the engine and 43t on the clutch = 1.955:1
So, 2.211:1 X 1.955:1 = 4.323 :1 drive ratio from engine to rear wheel
24t engine sprocket gives a ratio of 3.962:1

HTH
John